How Maglevs Work

by Barbara Saffer

A brief review of magnets will help explain how maglev (magnetic levitation) trains work. Every magnet has a north pole and a south pole. Similar poles of two magnets repel each other; opposite poles attract each other. These principles govern the levitation of maglev trains.

Permanent magnets are always magnetic. Electromagnets are magnetic only when an electric current flows through them. The north and south poles of an electromagnet are related to the direction of the current. If the direction of the current is reversed, the poles are reversed.

In maglevs that levitate by magnetic repulsion, the train lies over the guideway. Magnets on top of the guideway are oriented to repel similar poles of magnets in the bottom of the maglev. This pushes the train upward into a hovering position. This system is designed for maglevs that contain groups of extremely powerful superconducting electromagnets. These magnets use less electricity than conventional electromagnets, but they must be cooled to very low temperatures—from −269 degrees Celsius to −196 degrees Celsius.

In maglevs that levitate by magnetic attraction, the bottom of the train wraps around the guideway. Levitation magnets on the underside of the guideway are positioned to attract the opposite poles of magnets on the wraparound section of the maglev. This raises the train off the track. The magnets in the guideway attract the wraparound section only strongly enough to raise the train a few centimeters into a “floating” position. The wraparound section does not touch the guideway. (Imagine a C-shaped bracelet floating around your wrist without touching it.)

To picture how a maglev train is propelled forward, think of three bar magnets lined up on the floor. The magnet in front is pulling with an attracting (opposite) magnetic pole and the magnet in back is pushing with a repulsing (similar) magnetic pole. The magnet in the middle moves forward. A maglev's guideway has a long line of electromagnets. These pull the train from the front and push it from behind. The electromagnets are powered by controlled alternating currents, so they can quickly change their pull and push poles, and thus continually propel the train forward.

Vocabulary

levitation:

The state of rising and floating in the air in apparent defiance of gravity.

repulsion:

The tendency of particles or bodies of the same electric charge or magnetic polarity to separate.

Activity

What role does electricity play in powering maglev trains?[anno: Electricity is used to create electromagnets. The electromagnets are used on the track for a maglev train.]

Some maglev trains are levitated by magnetic repulsion. Other maglev trains are levitated by magnetic attraction. Describe how the magnets for magnetic repulsion are used differently than the magnets that are used for magnetic attraction.[anno: The magnets that are used for magnetic repulsion are placed on top of the guideway and repel the poles located on the bottom of the maglev train. The magnets that are used for magnetic attraction are placed underneath the guideway and attract the poles of the part of the train that wraps around the guideway.]

Imagine that instead of cars, people had small passenger vehicles that used propulsion and levitation magnets. What would be needed in order to make this system useful for transporting people from their homes to other places? What might be some benefits of this kind of system? What might be some drawbacks? Write a paragraph describing how a maglev system for passenger vehicles might work.[anno: Answers will vary.]